One of the key psychological sources of growing inequality seems to lie in the differences between the culture and norms of the middle class, which are institutionalized in American society, and those of the working class, which are not.

In his latest book, Invisible Influence: The Hidden Forces That Shape Behavior, Jonah Berger, a marketing professor at The Wharton School of the University of Pennsylvania, discusses the ways in which our behavior is shaped by others and examines our constant struggle to be optimally distinct—not too different and not too similar.